Influence of Heavy-Atom Tunneling on Pericyclic Reactions in Biosynthesis: A Computational Study.

Understanding the kinetics of reactions in biosynthetic pathways requires accounting for the contribution of quantum mechanical tunneling to the rates. Whereas hydrogen tunneling in biology is well established, the extent of heavy-atom tunneling in biochemical reactions has been very little studied. We report computational results (M06-2X/cc-pVDZ) on rate constants for electrocyclic ring closures and [3,3] sigmatropic shifts, processes dominated by heavy-atom motions, that are proposed steps in the biosynthesis of four representative natural products.